The present disclosure relates to fixing devices that fix toner images on sheets and image forming apparatuses.
A fixing device in an image forming apparatus includes a fixing nip portion formed by a fixing roller and a pressure roller being pressed against each other. When a sheet passes through the fixing nip portion, the sheet is pressurized and heated, thereby fixing a toner image on the sheet, onto the same sheet. A fixing roller in which a metal belt (fixing belt) is fitted onto an elastic roller member is known as the fixing roller. The fixing belt is heated by induction heating manner.
The fixing belt has an inner diameter that is greater than an outer diameter of the roller member at room temperature, and there is a clearance between the fixing belt and the roller member in the fitted state. When the temperature rises due to the fixing device being operated, thermal expansion occurs in the roller member, whereby the fixing belt and the roller member come into close contact with each other. Before the close contact state occurs, the fixing belt may meander in the axial direction of the fixing roller. Therefore, the movement of the fixing belt in the axial direction needs to be regulated. Thus, disk-shaped regulation members having regulation surfaces opposing side edges of the fixing belt are mounted near the axial ends of the fixing roller.
Further, when the fixing roller is pressed against the pressure roller, the fixing belt is deformed into an ellipsoidal shape by a deformation amount corresponding to the clearance. In this deformed state, a length of the major axis of the ellipsoidal shape of the fixing belt may be greater than the outer diameter of the regulation members. In this case, the side edges of the fixing belt repeatedly contact with the outer circumferential edges of the regulation members, and the side edges of the fixing belt are more likely to be damaged. Therefore, it is known that outer circumferential walls that prevent the side edges of the fixing belt from moving outward of the regulation members in the radial direction are provided on the outer circumferential edges of the regulation members.